A pressure sensor using mechanical-electrical transduction comprises a mechanical pressure receiving member which is connected at one end with a pressure chamber in which the pressure is to be measured and which has a pin, a membrane, a Bourdon tube or another suitable transmitting means which generates a length change inside the pressure sensor corresponding to the pressure residing in the pressure chamber.
Inside the housing this moving portion of the pressure receiving member is provided with a permanent magnet which cooperates with a locally fixed Hall-effect sensor located in the housing.
According to the pressure prevailing in the pressure chamber the moving portion and thus the permanent magnet attached with it more or less moves further toward the Hall-effect sensor whereby the electrical resistance of the sensor changes.
The resistance change is detected by an electronic analyzer (amplifying meter) connected to the Hall-effect device and is converted into an electrical signal with which an electronic instrument, a meter, a regulating device or the like is controllable or reports the pressure.
A pressure sensor of this type is described in German Open Patent Application DE-OS 28 42 140.
Disadvantageously with this known pressure sensor, the measuring range is comparatively small. Of course, it is possible by use of other pressure receiving members to measure pressure over a larger measuring range, for example from 0 to 1000 bar. However, a very expensive electronic analyzer is needed to make use of this pressure sensor and is usually particularly expensive. This is because the Hall-effect sensor has a linear characteristic response curve only in a comparatively small region because the field strength of the magnet decreases with increasing displacement of the magnet nonlinearly and that decrease exceeds that of a simple direct proportionality relationship.
Accordingly, the resistance changes in the Hall-effect sensor on larger displacements of the magnet as would occur with a larger measuring range (with constant resolution) are correspondingly reduced and must be compensated by an expensive and susceptible electronic analyzer. The use of this high resolution electronic analyzer is problematical particularly in underground excavation (e.g. mining) application especially because of the high cost price.
The tough requirements there in regard to temperature, air moisture and vibration bring disturbing influences with them which can lead to inaccurate measurements or to complete breakdown of the apparatus.